December 6 2017

12:00 LSB 2320

Deron Burkepile
Department of Ecology, Evolution, and Marine Biology, UC Santa Barbara

Fishes as top-down and bottom-up drivers of coral reef community dynamics


Losses of corals worldwide emphasize the need to understand what drives reef decline. Stressors such as overfishing and nutrient pollution that alter natural patterns of top-down (i.e. herbivory) and bottom-up (i.e. nutrient availability) processes likely impede reef resilience via increasing coral-algal competition. Algal competition reduces coral recruitment, growth, and survivorship by several mechanisms, including shading, abrasion, allelopathy, and disruption of coral microbiomes. Our lab has addressed several aspects of altered top-down and bottom-up forcing on reefs. We have shown that removals of important herbivorous fishes increases competition between corals and algae. Corals contacting algae suffered destabilized microbiomes, elevated pathogen loads, >2-fold more disease, and >8-fold more mortality. Above-average temperatures exacerbated these effects, further disrupting microbiomes of unhealthy corals and concentrating 80% of coral mortality in the warmest seasons. This work suggests strong interactions between global (increasing sea surface temperatures) and local (overfishing and nutrient pollution) stressors in driving coral morality on reefs. Our lab also focuses on the role of fishes as sources of nutrients in coral reef systems. We show that fish excretion can be the most important source of nitrogen and phosphorus on reefs. These fish-derived nutrients can determine patterns of coral and algal abundance, coral-algal competition, and foraging behavior of herbivorous fishes. Thus, fishes are important drivers of both top-down and bottom-up forces on reefs.











































































































































































































































































































































































































































































































































































































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